Deposition Mechanism And Spatial Deposition Characteristic Of 7YSZ Coating Prepared By PS-PVD

Thermal barrier coating(TBC),super-alloy and air cooling technique are known as three key technologies to manufacture the aero engine turbine blade.Over the past 50 years,the contribution of thermal barrier coatings cannot be ignored in the development of aero-engine.In the new period,the development of aero-engine to high thrust and high efficiency will inevitably lead to the further improvement of the working temperature in the engine combustion chamber.Therefore,the new generation of ultra-high temperature resistance,long life and high thermal insulation TBCs urgently needs to be researched and developed.Using traditional technology to prepare the thermal barrier coatings cannot meet the severe requirements in future high-performance engine,so new TBC preparation technologies must be developed,among which PS-PVD process is one of the most potential techniques.At present,it has been developed to a bottleneck stage that PS-PVD prepares thermal barrier coating.It is becoming increasingly difficult to improve the performance of the coatings by adjusting the parameters.Therefore,it is necessary to study PS-PVD deposition characteristics and coating growth mechanism.Moreover,understanding the growth process and influencing factors of PS-PVD TBCs(especially PS-PVD YSZ columnar structured coating),will provide theoretical support to control microstructure and properties of coating and eventually develop to meet the requirements of a new generation of TBCs.In this paper,the 7YSZ columnar coatings were prepared by PS-PVD in the form of stepwise deposition,radial deposition and axial deposition.The differences on the microstructure and properties of the coatings were studied by SEM,XRM,TEM,XRD and 3D profiler.Combined with OES diagnostic and numerical simulation,the coating growth model and PS-PVD axial and radial deposition model were established.Finally,the deposition mechanism and spatial deposition characteristics of PS-PVD 7YSZ columnar structure coating were discussed.In addition,the non-line-of-sight deposition characteristics of PS-PVD were studied through deposited on multi-vanes blades,which laid the foundation for the future engineering application.Details are as follows.(1)The growth evolution of typical PS-PVD 7YSZ columnar coating was studied adopting a stepwise deposition experiment.The results indicated that the columnar coating growth process can be divided into three stages.These stages are:stage I,a dense coating composing of well-ranged fine columns is formed through absorption,nucleation and growth;stage Ⅱ,this is the fastest deposition stage,fine columns grow rapidly up to large columns with big gaps in between;stage Ⅲ,the typical columnar structures are formed eventually after new column branches growing on large column.Entering into stage III,the formation and inhibition of the column branches on the coating surface reach a dynamic equilibrium,meanwhile the porosity,roughness and thermal conductivity of the coating tend to be stable.(2)The regional deposition characteristic of PS-PVD 7YSZ process was investigated through radial deposition method.The results show that the coating along the radius of plasma jet could be divided into three typical zones:in the zone I,the coating is all composed of columnar structures with cauliflower structure,which is dominated by the deposition of gas phase;in the zone Ⅲ,the coating made up of partially-molten particles mainly without columnar structures;the zone II is between the zone I and the zone Ⅲ,in which there are columns with domed top and small particles.Combined with OES diagnostic,preliminary models about the state and distribution of the powder particles in expanded Ar-He and Ar-He-H2 plasma jet were proposed.Most gas phase distributes in the center of plasma jet;the proportion and size of partially-molten particles increases with the radius increasing.Compared to Ar-He,there are more extensive distribution of gas phase and higher proportion of partially-molten particles in the Ar-He-H2 jet.(3)PS-PVD 7YSZ coatings were fabricated at different axial positions,which suggest that PS-PVD 7YSZ coating is controlled by non-spontaneous nucleation and spontaneous nucleation.The coatings prepared at spray distances 350 mm and 1800 mm exhibit dense structure,in which the former is developed under the combination effect of the supersaturated spontaneous nucleation from high concentration of gas phase and liquid/solid particles and the latter is accumulated from gas phase spontaneous re-solidified particles;in the range of 650～1250 mm,typical 7YSZ columnar coatings were formed,which are dominated by the non-spontaneous nucleation after the deposition of gas phase on the substrate,and supplemented by spontaneous nucleation in plasma jet.Under the effect of spontaneous nucleation,the microstructure differences among columnar coatings appear in stage Ⅲ.(4)It is found that the intrinsic properties of PS-PVD jet affect coating deposition significantly via PS-PVD deposition experiment based on stand-off distances and deposition angles.The temperature and velocity of jet near the substrate have an important impact on the formation and growth of nuclei.In addition,the deposition efficiency of the coating is related to the pressure distribution of plasma jet on the substrate surface,the higher pressure,the higher deposition efficiency;the direction and degree of oblique angle of columnar structures is dominated by the direction and value of the jet velocity,respectively.(5)NiCoCrAlYTa metallic protective coating and TBC were deposited on multi-vanes blades for the gas turbine and the aero-engine via PS-PVD process,respectively.The results show the entire surfaces of two blades were coated high quality and good uniformity coatings,and the ratio of the thinnest and thickest thickness coatings was 1:2,which means PS-PVD process have a good non-line-of-sight deposition characteristic.